Packaging Technology for an Implantable Inner Ear MEMS Microphone

Abstract

Current cochlear implant (CI) systems provide substantial benefits for patients with severe hearing loss. However, they do not allow for 24/7 hearing, mainly due to the external parts that cannot be worn in all everyday situations. One of the key missing parts for a totally implantable CI (TICI) is the microphone, which thus far has not been implantable. The goal of the current project was to develop a concept for a packaging technology for state-of-the-art microelectromechanical systems (MEMS) microphones that record the liquid-borne sound inside the inner ear (cochlea) as a microphone signal input for a TICI. The packaging concept incorporates requirements, such as biocompatibility, long-term hermeticity, a high sensing performance and a form factor that allows sensing inside the human cochlea and full integration into the existing CI electrode array. The present paper (1) describes the sensor packaging concept and the corresponding numerical and experimental design verification process and (2) gives insight into new engineering solutions for sensor packaging. Overall, a packaging concept was developed that enables MEMS microphone technology to be used for a TICI system.

Round Window Reinforcement-Induced Changes in Intracochlear Sound Pressure

“…Both numerical models considered in the present study are LEMs that rely on the analogy between electrical, mechanical, fluidic, and acoustic domains to describe the behavior of a specific physical system as a circuit of lumped elements. The analogy only holds if the wavelength of the sound wave in the given system's fluidic or solid medium is much larger than the largest geometrical dimension of the system [22]. A LEM of the cochlea transforms its fluid dynamic behavior into an electrical system and represents the fluidic characteristics by electrical components: inductors (L), capacitors (C), and resistors (R).…”

Novel Fabrication Technology for Clamped Micron-Thick Titanium Diaphragms Used for the Packaging of an Implantable MEMS Acoustic Transducer

“…Excessive loading of the PD by ambient pressure changes can lead to a varying or not tolerable loss in sensing performance. A deeper discussion of that problem and a proposal for a system that can maintain pressure equalization in a hermetically sealed microphone system are given in [6].…”

“…Schematic drawings of a MEMS microphone and the corresponding ASIC packaged in a biocompatible and hermetic Ti enclosure with a PD that can transfer the sound energy to the MEMS transducer. (a) A generic enclosure geometry with one larger PD located directly in front of the MEMS microphone diaphragm; (b) a more specific enclosure geometry that was developed for an intracochlear acoustic receiver [6]. Four PDs are integrated into a tube-like part of the enclosure to allow the recording of the liquid-borne sound pressure in the human inner ear with sufficiently high receiving sensitivity.…”

“…A practical example of a packaging concept that illustrates these design guidelines is the intracochlear acoustic receiver (ICAR), which is currently under development by our group [6,8]. The receiver is designed to be used as an implantable microphone solution for a fully implantable cochlea implant.…”

“…Multiple PDs free of intrinsic stress are required to minimize the loss in sensing performance caused by the encapsulation of the MEMS transducer. Using a theoretical model, a loss in sensitivity of approximately 10 dB was predicted below the resonance operation of the sensor at 3.5 kHz [6]. The inertia of the PDs that are in contact with the perilymph (similar to water) in the inner ear defines the resonance and limits the bandwidth of the ICAR to approximately 6 kHz.…”